This research is designed to study the mechanisms by which early maternal separation in the rat increases the animals' subsequent predisposition to develop gastric erosions during restraint. As part of this research we are studying the psychobiologic mechanisms by which physical restraint produces gastric erosions in the rat. We have previously shown that when rats are weaned at the customary time of 21 days postnatally and tested with restraint on day 30, the incidence of restraint erosions is near zero. When rats are weaned early, on day 15, and tested with restraint on day 30, the incidence of restraint erosions is about 90%. We are now using these "high risk" and "low risk" groups to study how the restraint produces gastric erosions. That is, during the restraint period we can compare selected parameters of behavior (e.g., activity and sleep), gastric physiology (e.g., acid secretion and gastric blood flow) and the central and peripheral regulatory processes relating them (e.g., temperature regulation). We are also studying specific factors in the early separation that increase subsequent lesion vulnerability at day 30. Behavioral factors in the mother-pup diad, nutritional factors, and the interaction between these are being investigated. BIBLIOGRAPHIC REFERENCES: Ackerman, S.H. and Weiner, H. Peptic Ulcer Disease: Some Considerations for Psychosomatic Research, in Modern Trends in Psychosomatic Medicine-III (O.W. Hill, Ed.), Butterworth, London, 1976, pp. 363-381. Ackerman, S.H. and Shindledecker, R. Factors in the Etiology of Restraint Erosions in Parabiotic Rats. Gastroenterology, 71: 426-428, 1976.